>Tau are planning 5th and 6th Sphere expansions to happen at the same time
>One of them in all likelihood will involve an invasion of Utlramar
>Most likely outcome is that they attack Ultramar in the 5th Expansion Sphere, Guilliman pulls a bunch of resources and armies from other parts of the Imperium to stop them, a long drawn out war of attrition happens where the Tau eventually are forced to retreat back into their own territory with the Expansion Sphere considered a failure
>Then it's revealed that the 6th Expansion Sphere was a massive success because of all the resources that were pulled to Ultramar allowing them to take thousands of worlds with little opposition
>Guiliman gets a win since he successfully defended Ultramar and only lost territory he doesn't care about, the Tau get a win since they got to massively expand their territory, and everyone's happy.
That's my personal prediction for how it'll turn out at least.

>>96538584
Like 99% of the Imperial Guard are the most elite PDF regiments that can be taken from the Hive worlds, who themselves take the elite 1% of their population to use as their PDF. The toughest, baddest hivers you can imagine, who eat iron and spit lead, given good equipment.